xISBN extensions

I think it's fair to say that xISBN (here's an application) has been a fairly popular service.  We've done quite a bit of work to make the results better, but little to explore what other types of services could extend or compliment it.  I recently posted a similar list to  Code4Lib, but thought an entry here might reach a slightly different group.

Here are a few ideas that either we've thought of, or have been proposed to us:

• ISBN to author/title or more extensive work-level metadata
• Adding 'distinctive' information to the response to help selection
• xOCLC: take in an OCLC number and return the OCLC numbers in its FRBR work-set
• xLCCN: do the same thing for LCCNs
• xISSN:  do the same thing for ISSNs
• SOAP wrappers around everything
• Expose services via OpenURL 1.0

Some of these would take more work than others.  the OCLC number and LCCN sound easy.  The author/title information probably isn't too hard, as we are doing similar things in FictionFinder.
Deciding what is distinctive for one ISBN versus the others in a work-set sounds a bit harder.  ISSNs sound hard, too.  Our FRBR algorithm does group some serials together, but FRBRizing serials is at least slightly contentious and we don't claim to have even a proposed solution, although we do see the need.

We're open to suggestions.  It would be nice to have some sort of premium service that would help sustain the free services.

--Th